Electrically alterable read-only semiconductor memories may be constructed using floating gate field effect transistors as storage cells in the core. Each cell is programmed by directing a higher than normal voltage programming pulse to the cell by way of a program line associated with the cell. Typically, the memory normally operates at 5 volts, while 20 volts is used for the programming pulse.
In the prior art, the program lines are normally in electrical communication with a suitable 20 volt source, the 20 volt signal being grounded out by means of a suitable transistor switch when no programming pulse is needed. When programming, only one program line is used at a time. That one program line is activated to produce a programming pulse by turning off the grounding transistor so that the program line may rise to 20 volts. All the rest of the program lines remain grounded so that a small current always flows from the 20 volt source, to these program lines, and thence to ground. In larger memories there may be, for example, 256 program lines conducting a small current most of the time.
In the past, this current drain was too small to be of any concern. However, in the search for better, simpler, easier to use solid state memories, it would be desirable to eliminate the need for an external 20 volt supply and instead generate internally the 20 volts needed for programming, on the chip itself. Such a goal is possible only if the chip's 20 volt generator is not required to supply currents in the magnitudes previously accepted as normal. Hence, there is a need for a circuit that can more efficiently produce the programming pulse without wasting current while in the standby condition. This need is met by the present invention.